head to head
Yakuza 6: The Song of Life asks more than Grand Theft Auto V, and the gap is optimization.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
Kiryu's farewell chapter protecting a baby in seaside Onomichi.
Grand Theft Auto V leans Execution (Practiced Mastery); Yakuza 6: The Song of Life leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Yakuza 6: The Song of Life
Simplified Dragon Engine combat keeps a light timing test.
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Yakuza 6: The Song of Life
Enemies follow fixed scripts.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Yakuza 6: The Song of Life
Negligible randomness.
Yakuza 6: The Song of Life leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Yakuza 6: The Song of Life
Stat feeding and heat upgrades are straightforward systems.
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.